A Developer's 24-Year Habit: Write Three Lines, Then Run Them

A software developer describes a coding discipline they have practiced for 24 years: writing just three lines of code at a time before running and verifying the result. The approach is built on three principles — trusting only code you can personally verify, expressing logic directly in code rather than natural language, and making each small unit complete with error handling and validation from the start. The author argues that three lines represent the maximum unit of thought a programmer can fully hold in mind, and that writing more without testing causes a dangerous gap between the code imagined and the code actually running. When integrating unfamiliar libraries or APIs, the same method applies — probing the component in tiny increments to understand its behavior before incorporating it into real work. The discipline keeps debugging fast and focused, since any problem can be traced to the most recent three-line change rather than requiring an archaeological dig through dozens of untested lines.